The envelope of gases that surround our Earth and allow life, as we know it, to exist is called "the atmosphere". The current atmosphere is the product of 4. This topic investigates the physical structure and properties of the atmosphere, while the topic The composition of the Earth's atmosphere , investigates the origins and gases of our atmosphere.
Atmospheric layers The atmosphere extends some km into space from the Earth's surface. It is made up of five physical layers - the troposphere, stratosphere, mesosphere, thermosphere and exosphere, each with distinctly individual properties.
Two other regions - the ionosphere and magnetosphere - exist within these layers. Both are the product of interaction between the Sun and Earth's atmosphere.
One factor best distinguishes one layer from another - temperature. Each layer behaves differently from its neighbours with respect to the temperature and how temperature varies within the layer. These layers and regions will now be investigated starting with the layer closest to the Earth's surface, the one we are most familiar with because we live in it - the troposphere.
Troposphere The troposphere contains over half of the air in our atmosphere and extends up to 20 km above the Earth's surface at the equator. The mesosphere extends from altitudes of about 50 km 31 mi to 85 km 53 mi.
In this layer, the air pressure is only about 1 percent of what it is at sea level, but that is still enough air to burn up meteors. At the top of the mesosphere — the mesopause — scientists have recorded the coldest temperatures in the atmosphere.
They are around C F. In the top layer of the atmosphere, the thermosphere, temperatures again rise with altitude due to absorption of ultraviolet sunlight. At the top of this layer, temperatures can vary from C F to 2, C 3, F or higher. The high energy radiation from the sun ionizes particles in this layer, and for this reason, it's sometimes referred to as the ionosphere. It's the layer in which the auroras occur. Some scientists identify a fifth layer that begins above the thermosphere and extends from , to , km 62, to , mi into space.
In this layer, called the exosphere, the air density gradually trails off to nothing. Although there is no clear gradient, temperatures can vary from 0 C 32 F to 1, C 3, F depending on whether it's day or night, The concentration of particles is too low to conduct heat, however. Chris Deziel holds a Bachelor's degree in physics and a Master's degree in Humanities, He has taught science, math and English at the university level, both in his native Canada and in Japan.
Gas molecules are able to move freely and if they are uncontained, as they are in the atmosphere, they can take up more or less space. Warmer, lighter air is more buoyant than the cooler air above it, so it rises. The cooler air then sinks down, because it is denser than the air beneath it. This is convection, which was described in the Plate Tectonics chapter. The property that changes most strikingly with altitude is air temperature.
Unlike the change in pressure and density, which decrease with altitude, changes in air temperature are not regular. A change in temperature with distance is called a temperature gradient. The temperature gradient of each layer is different. In some layers, temperature increases with altitude and in others it decreases. The temperature gradient in each layer is determined by the heat source of the layer Figure below.
The four main layers of the atmosphere have different temperature gradients, creating the thermal structure of the atmosphere. The layers of the atmosphere appear as different colors in this image from the International Space Station. Most of the important processes of the atmosphere take place in the lowest two layers: the troposphere and the stratosphere. The temperature of the troposphere is highest near the surface of the Earth and decreases with altitude. On average, the temperature gradient of the troposphere is 6.
What is the source of heat for the troposphere? The temperature is also higher near the surface because of the greater density of gases. The higher gravity causes the temperature to rise. Notice that in the troposphere warmer air is beneath cooler air. What do you think the consequence of this is? This condition is unstable. The warm air near the surface rises and cool air higher in the troposphere sinks.
So air in the troposphere does a lot of mixing. This mixing causes the temperature gradient to vary with time and place. Sometimes there is a temperature inversion , air temperature in the troposphere increases with altitude and warm air sits over cold air. Inversions are very stable and may last for several days or even weeks.
Inversions form:. Since temperature inversions are stable, they often trap pollutants and produce unhealthy air conditions in cities Figure below.
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